Preparation of p-acylstyrenes



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PREPARATION OF p-ACYLSTYRENES No Drawing. Application November 29, 1952,

. Serial No. 323,335

1' Claim. (Cl. 260-592) This invention relates to the preparation of p-acylstyrenes. More particularly, this invention relates to the simultaneous preparation of p-vinyl'acetophenone, p-di- "acetylbenzene, and p-divinylbenzene.

In my copending application Serial No. 246,524, filed September 13, 1951 (now abandoned), the method of preparing p-vinylacetophenone from p-acetylphenylmethylcarbinol acetate is described.

I have now found that p-acylphenylmethyl carbinols can be dehydrated to produce the corresponding p-acylstyrenes.

It is, therefore, an object of my invention to provide a method of preparing: p-acylstyrenes. Another object is to provide a method of preparing p-vinylacetophenone. Still another object is to provide a method of simultaneously preparing p-vinylacetophenone, p-diacetylbenzene and p-divinylbenzene. Other objects will become apparent from a consideration of the following description andexamples.

The p-acylstyrenes obtained according to my invention are useful in the preparation of synthetic resins. Certain derivatives of these resins are characterized by light-sensitive properties, which can be utilized in the photographic art.

According to my invention, I obtain p-acylstyrenes by dehydrating a p-acylphenylmethyl carbinol selected from those represented by the following general formula:

wherein R representsan :alkyl group, e. g. methyl, ethyl, n-propyl, isopropyl, etc. The dehydrations are advantageously effected at a temperature of from 150-600 C. Temperatures of from 250500'C. have'been found to be especially useful.

The dehydrations are advantageously eifected in the presence of a dehydration catalyst, such as phosphorus pentoxide, alkali metal-bisulfates (sodium bisulfate, potas-' sium bisulfate, etc.), alumina (aluminum oxide), silica; glass, silica gel, etc. Alumina has been found to be-particularly useful, especially for the dehydration. of p-acetylphenylmethyl carbinol, since itprovides not only the desired p-vinylacetophenone, but also p-diacetylbenzene and p-divinylbenzene. Both-of the latter products are desirable and useful.

The following examples will serve to illustrate more fully the manner whereby I practice my invention.

In a standard Parr low-pressure hydrogenation appara-tu's there were placed 64.8 grams (0.4 mole) of pdiacetylb'enzene, 32 grams of freshly prepared, alcohol- Washed Raney nickel, and 175 cc.- of methanol. The reaction vessel was evacuated and flushed three ti-r'nes with hydrogen in. the usual way and pressured to 50 p. s. i. After shaking for 32 minutes the pressure dropped 30 pounds at which time shaking was stopped. (Theory 29 lbs.) The catalyst was removed and the reaction mixture evaporated at the water pump.

No attempt was made to separate the products, but the reaction mixture was acetylated directly by heating with 150 cc. acetic anhydride and 5 cc. pyridine on the steam cone for 16 hours. Distillation through a 6-inch Vigreux-type column resulted in the following fractions:

2, 4-dinltr0- No. B. P., C. phenyl hydrazine test 1 94/1.0 mm +red. 2 113ll6/0.7 mm +yello'w; 3; .1169/0.7mn"1 +ye11ow'; 4 1l8/0.75 mm +yellow.

Fraction 2 (presumably diacetyl benzene) partially crystallized and crystals of itwere filtered 01f and melted at 10440'7" C.- after pressing on a porous plate. Fractions 2, 3 and 4 were combined (71 grams) and redistilled' to give the following fractions:

Fraction 1 was probably'p-e'thyl acetophenone, Fraction- 8 was the acetate of p-acetoph'enyl methyl carbinol.

Example 2.-p-Acetylphenylmethyl carbinol 0 ijk-CHi' A mixture of grams (0.485 mole) of p-acetylphenylmethyl carbinol acetate, 250 cc. of methanol and 1.0 gram of sodium-methoxide was allowedto stand: at room temperature (28* C.) for one-half hour during-which time the reaction-mediurnturnedgreen. The reaction'mixtu're 13. P., C. 7141 Weight,

grams This represents a total of 61 grams (76.8 percent) of p-acetylphenylmethyl carbinol.

Analysis.Calculated for CmHmOz: C, 73.1; H, 7.4. Found: C, 72.7; H, 7.7.

The 2,4-dinitrophenylhydrazone was prepared and after recrystallization from alcohol and water melted at 204-205" C. Recrystallization from hexane gave the same melting point.

Example 3.-Dehydratin of p-acetylphenylmethyl carbi- Harshaw activated alumina Al-Ol04T--% inch was preheated in a stream of air for six hours at 550 C. The catalyst was cooled to 480 C. and used immediately as follows:

One hundred grams (0.61 mole) of p-a'cetylphenylmethyl carbinol was passed dropwise at one drop per two sec. through a 25-mm. O. D. Pyrex tube packed for a distance of one inch with glass beads, followed by 28 inches of the above catalyst and finally with one inch of glass beads, and heated to 480490 C. by means of an electrically heated furnace. The reactants and products were swept through the tube by means of dry nitrogen flowing at the rate of six liters per hour. Several Dry Ice traps were required to condense the gaseous products. The combined condensates were diluted with 200 cc. of benzene, ten grams of water was separated and the organic material dried over anhydrous magnesium sulfate. After the addition of a trace of picric acid the benzene was removed at the water pump. An equal volume of hexane was added to the residue and after cooling in crushed ice, six grams of a white solid, M. P. 109ll0 C., was filtered off. This material was p-diacetylbenzene as determined by a. mixed melting point, with an authentic sample of p-diacetylbenzene.

The hexane was removed from the mother liquors at the water pump and the residue distilled in vacuo through a 6-inch Vigreux type column to yield the following fractions:

B. P., C. 111, M. P. of mass, C.

. 8.53 grams, M. I. 410.

Wt. 8.6 grams, 22.5-24.5". wt. 15.5 grams, 24-28".

M. P. 34-35" C. when recrystallized from hexane. Similarly, fraction 5 recrystallized from 15 cc. hexane gave 10 grams of p-vinylacetophenone. Total yield 16.8 grams (20.9 percent).

One-gram portions of the following fractions were titrated for unsaturation by the standard bromide-bromate technique, using N solution:

Cc. of bromide-bromate Fractions 1, 2, 3 combined 46.7 Fraction 4 26.19 Fraction 5 24.57 Pure p-vinylacetophenone 28.0 Pure styrene 38.75 3,4-dimethyl styrene 30.13

As can be seen from the above data, fractions 1, 2 and 3 (combined) consist largely of p-divinylbenzene. This material can be used directly in the preparation of synthetic resins.

In a manner similar to that illustrated in Example 3, p-butyrylphenylmethyl carbinol can be dehydrated to produce p-butyryl styrene. Also, catalysts other than alumina can be employed in the dehydration, as has been shown above.

The intermediates represented by Formula I above can advantageously be prepared by hydrolysis of the corre sponding acetates, as illustrated in Example 2 above. The p-acylphenylmcthyl carbinol acetates can advantageously be prepared by hydrogenation of p-alkylacetophenone, followed by acetylation of the carbinol thus produced, and oxidation of the carbinol acetate in the presence of air and chromium sesquioxide and calcium carbonate (as oxidation catalysts) as shown in application Serial No. 246,524 mentioned above.

The particular temperature used will depend somewhat on the catalysts selected and the time of contact between the p-acylphenylmethyl carbinol and the catalyst. The carbinols can be directed through the dehydration apparatus by means of an inert gas, such as nitrogen, carbon dioxide, etc.

The 2,4-dinitrophenylhydrazone, melting at 204205 C., obtained in Example 2 had the following analysis:

Calculated for C14H16N4052 C, 55.8; H, 4.7; N, 16.3. Found: C, 55.8; H, 5.0; N, 16.3.

I have also found a new method of preparing p-divinylbenzene, which comprises heating 1,4-bis(a-hydroxyethyl)benzene diacetate at a temperature of 500550 C. The following example briefly describes such a process.

Example 4 A mixture of 13.5 g. (0.065 mole) of p-(a-hydroxyethyl)phenylmethyl carbinol acetate, 20 g. (0.2 mole) of acetic anhydride and 5 drops of pyridine was heated on the steam cone for 16 hours. Distillation of the reaction mixture yielded 21.0 g. of the diacetate, boiling at 104 C./0.2 mm., 11 1.4955. A sample prepared from p-diacetyl benzene had the same constants.

A solution of 21.0 g. (0.084 mole) of 1,4-bis(o-hydroxyethyl)benzene diacetate in 25.0 cc. of benzene was passed dropwise during the course of one and one-half hours through a 25 mm. 0. D. Pyrex tube packed for a distance of 30 inches with glass beads and heated to 525-535 C. by means of an electrically controlled furnace. The reaction products were swept into a Dry Ice trap by a slow stream of nitrogen. The reaction products were melted, washed With water and dried over anhydrous magnesium sulfate. Distillation yielded 7.7 g. (70%) of p-divinylbenzene, boiling point 34 C./ 0.2 mm. Titration of 0.52 g. of this material with molar bromide-bromate solution required 30.2 cc. corresponding to a purity of 97.6 percent.

In general, the method of Example 4 is not as advantageous as that described in Example 3 above.

What I claim as my invention and desire secured by Letters Patent of the United States is:

A process for simultaneously preparing p-vinylacetophenone, p-diacetylbenzene, and p-divinylbenzene c0rn prising heating p-acetylphenylmethyl carbinol at a temperature of from 480-490 C. in the presence of alumina, and thereafter separating the p-vinylacetophenone, p-diacetylbenzene, and p-divinylbenzene from the reaction mixture.

References Cited in the me of this patent UNITED STATES PATENTS Butler Mar. 2, 1954 

